Exciter and Quadrature Error Correction Method

1. An exciter comprising: a sine wave generator configured to generate a first sine wave and a second sine wave having a phase different from the phase of the first sine wave by 90.degree. while changing a frequency in a predetermined step at a preset time interval; a filter configured to store a plurality of filter coefficients, set one of the plurality of filter coefficients, and perform filter processing for the first sine wave and the second sine wave using the set filter coefficient; a digital/analog converter configured to convert the first sine wave and the second sine wave after the filter processing into a first analog signal and a second analog signal, respectively; and a quadrature modulator configured to quadrature-modulate the first analog signal and the second analog signal and generate a modulated signal according to the frequency at which the first sine wave and the second sine wave are generated, wherein the plurality of filter coefficients have delay differences necessary for a rangy e and a resolution to correct a skew difference of IQ signals in the quadrature modulator.

2. The exciter according to claim 1 , further comprising a modulation processor configured to convert an input signal into an I signal and a Q signal in a baseband, wherein the filter performs the filter processing of the I signal and the Q signal using the filter coefficient suitable to correct a skew difference of IQ signals in the quadrature modulator, the filter coefficient being set based on a result of spectrum analysis of the modulated signal according to a plurality of frequencies, the digital/analog converter converts the I signal and the Q signal, which have undergone the filter processing, into a third analog signal and a fourth analog signal, respectively, and the quadrature modulator quadrature-modulates the third analog signal and the fourth analog signal.

3. The exciter according to claim 1 , wherein the exciter is connectable to a spectrum analyzer.

4. A quadrature error correction method comprising: generating a first sine wave and a second sine wave having a phase different from the phase of the first sine wave by 90.degree. while changing a frequency in a predetermined step at a preset time interval; performing filter processing for the first sine wave and the second sine wave using a filter coefficient set out of a plurality of filter coefficients stored in advance, wherein the plurality of filter coefficients have delay differences necessary for a range and a resolution to correct a skew difference of IQ signals in a quadrature modulator; converting the first sine wave and the second sine wave after the filter processing into a first analog signal and a second analog signal, respectively; quadrature-modulating the first analog signal and the second analog signal and generating a modulated signal according to the frequency at which the first sine wave and the second sine wave are generated; and outputting the modulated signal according to a plurality of frequencies to a spectrum analyzer.

5. The quadrature error correction method according to claim 4 , further comprising: when the filter coefficient suitable to correct a skew difference of IQ signals in the quadrature modulation is set based on a result of spectrum analysis of the modulated signal according to the plurality of frequencies by the spectrum analyzer, performing the filter processing using the set filter coefficient for an I signal and a Q signal in a baseband converted based on an input signal; converting the I signal and the Q signal after the filter processing into a third analog signal and a fourth analog signal, respectively; and quadrature-modulating the third analog signal and the fourth analog signal.